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From: OddBALL <odd@ball.net>
Newsgroups: alt.binaries.pictures.totty
Subject: Re: Resizing using Thubsplus - IMG_0140.jpg (0/1)
Date: Sat, 22 Feb 2014 14:46:47 -0800
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On 19 Feb 2014 22:22:59 GMT, Gumby Gump <gumby.gump@domain.invalid>
wrote:
>On Tue, 18 Feb 2014 09:58:50 -0800, OddBALL wrote:
>
>
>> Thank you, I will check out thumbsplus.
>
>If you do, and you decide to destroy the images by resizing (yep, they
>ORIGINALS! Mark them clearly as being tampered with.
>
>copy, then tell me there is no difference. It is a well-known fact that
>JPEG has destructive compression. And it is especially prominent when you
>resize an image, which will be explained further down.
>
>The compression in JPEG is, in short, done by dividing the image up in to
>8 by 8 pixel squares, and depending on your compression setting, the
>compression algorithm will try to make those 8 by 8 pixels more and more
>alike, because the more alike the colors are the easier it is to get a
>high compression ratio. Compare with an image having a single color, like
>clear sky, and an image having lots of detail, like hair. Guess which
>compresses the most?
>
>Therefore you can see the, what is known as, JPEG artifacts as an 8 by 8
>pixels pattern all over the compressed image. More prominent the more
>compression was used (not to be confused with some applications'
>"quality" setting, which is the inverse of compression, i.e. the more
>quality the less compression is used).
>
>A JPEG with no, to very little, compression, has far less of these
>artifacts, and this is clearly visible if you zoom in to the individual
>pixels.
>
>So, therefore, if you resize an image, the 8 by 8 square will not be at
>the same place as it was on the original and you will get interference
>between the pixels which will further degrade the image.
>
>Then, two years from now, some other person decides that they are either
>still too large, or they are too small, so they are resized yet again,
>and at the same time maybe color "enhancement" is introduced. And then
>the you-know-what really hits the fan.
>
>We've all seen old images floating around on the web or in groups, images
>which were produced quite a number of decades ago where all the color has
>taken on a yellowish-red tint which cannot be removed all that well, and
>they are over-compressed so you can see the JPEG artifacts clearly all
>over the image. Or other, strange "enhancements" like "repairs" have been
>made. [yuck!]
>
>It is a bad idea to resize original images. And especially JPEGs.
>
>This is all I have to say about this. Personally, I prefer original
>images over destroyed copies.
I think you misunderstand what I mean by original.
Professional photographers work with file sizes and types that are
probably beyond your comprehension. (nothing personal) For example,
the originals are in NEF file and each picture is over 40 mb. Not only
are they way too big to post, but you wouldn't be able to open them
without specialized software.
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